Four British Royal Marines have been killed in two separate explosions in southern Afghanistan.
Three are believed to have died in a suspected suicide attack carried out by a 13-year-old boy, while another died in a roadside bombing.
British Prime Minister Gordon Brown has made a surprise visit to troops in Helmand Province in Afghanistan. He condemned the Taliban for using a child suicide bomber.
'It is a terrible commentary on the Taliban that they should use a 13-year-old child as a suicide bomber to kill some of our British troops,' an emotional Mr Brown told scores of British soldiers gathered around him at their Camp Bastion base.
'We have been through difficult times as a result of a change of tactics by the Taliban,' Mr Brown said, referring to increased Taliban violence that has raised concern in Europe.
Mr Brown thanked the soldiers for their courage, saying there was a chain of terror that ran from the mountains on the Pakistan-Afghan border 'and could end up in the cities and towns of Britain'.
Mr Brown was then flown by helicopter to visit an observation tower near the town of Musa Qala which overlooks Taliban territory. He then spoke to British soldiers there from a Gurkha regiment and local officials, including a chief of police who was a Taliban member until year ago.
Obama vows to prioritise Afghanistan
British soldiers said it was the closest a British prime minister had got to the frontline in Afghanistan. Mr Brown then flew to the Afghan capital, Kabul, for talks with President Hamid Karzai.
British military and government sources said Britain has reinforced its 8,100 forces in Afghanistan with about 300 troops to press a campaign against the Taliban in the area around Lashkar Gah, the provincial capital of southern Helmand province.
The have formed a new battle group with Danish and Estonian forces of nearly 500 to fight the Taliban around Lashkar Gah, a military source said.
The battle group has launched a major operation to clear the Taliban from the area after insurgents tried to mount a large scale attack on local government installations in October, but were repulsed, the source said.
US President-elect Barack Obama has pledged to make Afghanistan a top priority. The US is sending 3,000 extra troops to the country and is considering whether to send up to 20,000 more in the next 12 -18 months.
The British military source said between 6,000 and 10,000 US troops would be sent to Helmand.
Britain has said it will consider any request from Sen Obama for more troops although it stresses there must be a fair sharing of the burden among NATO allies.
British generals complain that British forces are stretched by fighting in Afghanistan and Iraq and have been reluctant to take on new commitments. A defence source said this week that Britain could start withdrawing most of its remaining 4,000 troops from Iraq from March next year.
The defence officials say British troops will not be redeployed in large numbers to Afghanistan because troops need a break between deployments.
